Research is concerned with the neurophysiological mechanisms involved in voluntary and reflex control of jaw movements in intact, unanesthetized, animals. Monkeys are trained to control either incisal biting force or jaw position by having them observe a visual spatial representation of either of these variables and keep the visual feedback signal within a visual target zone. In some cases, sinusoidal perturbations of the load or position are imposed by a servo mechanism to study the reflex regulation of these variables. Activity of jaw muscle spindle afferents or neurons of the face area of the precentral cortex is studied in relationship to these behaviors. Selective lesions of these structures are produced to determine their contribution to the properties of jaw control. Neural recording and lesions in various structures of the brain of the guinea pig will be used to study the subcortical neural mechanisms involved in the production of jaw movement and muscle activity patterns associated with mastication.